Geology on an epic scale: the Yellowstone caldera

To those with even a little geological knowledge, the view that presents itself as you drive into Yellowstone National Park through the South Entrance may not be quite what you expect. The park encompasses the giant caldera of a hotspot-fuelled ‘supervolcano’ that last exploded 630,000 years ago, and is famous as the place to see geysers, hot springs and other hydrothermal activity, all powered by that same hotspot. So it is perhaps a little disappointing that all that initially presents itself is a sea of lodgepole pine (and, when I visited, snow on the ground). Pretty, but not exactly…dramatic.

South Yellowstone, near Lewis River

South Yellowstone, near Lewis River. Photo: Chris Rowan, 2010

It does not take long, however, for signs of Yellowstone’s unique volcanic nature to make themselves apparent. In places, the pine-filled horizon is broken by rising plumes of steam from geysers and hot springs.

Geyser, Norris Basin. Photo: Chris Rowan, 2010

In some regions, the forest gives way completely to a bubbling, steaming hydrothermal wasteland.

Firehole River, near Upper Geyser Basin (click for larger version). Photo: Chris Rowan, 2010

Indeed, the whole area is dynamic and ever-changing: new hot springs and fumaroles can pop up almost anywhere.

A new vent burns through a parking lot. Photo: Chris Rowan, 2010

However, despite the ample evidence of the large amounts of thermal energy just beneath your feet, the fact that you are effectively standing in the crater of a giant volcano remains a bit abstract and difficult to grasp, mainly because you can’t easily see that crater. The big hole in the ground left by the last explosive eruption 630,000 years ago has been largely filled in by later eruptions of rhyolite lava; the topography has been smoothed by the waxing and waning of ice sheets during recent glaciations. During my visit, I was on the lookout for a large cliffs that might mark the caldera rim, but although there were cliffs aplenty, they generally turned out to be formed of (relatively) young rhyolite.

Rhyolite cliffs overlooking Madison River, W Yellowstone (click for larger version). Photo: Chris Rowan 2010

This does give an inkling of the scale of the geological forces at work in this region: the cliff photographed above represents a ‘minor’ flow that followed the last big explosive eruption, yet it is still getting on for 100 m high. But to really get to grips with the scale of the geological processes operating in Yellowstone, actually standing in it is perhaps not the best vantage point. You really need to take a much wider view:

Topography of the area around Yellowstone, including the Snake River plain

If you look at the topography of the northwestern US, the Snake River Plain rather noticeably stands out as a wide channel cutting right through the Rocky Mountains. But this feature was not carved by any river. It is underlain by a line of now-extinct calderas: the oldest, to the west, was active more than 16 million years ago, and they get progressively younger to the east before the line intersects the active Yellowstone caldera.

Path of the Yellowstone hotspot

The chain of calderas left in the wake of the Yellowstone hotspot.

This line of ancient supervolcanoes records the passage of the Yellowstone hotspot – or, more accurately, the movement of North America over the Yellowstone hotspot – in the last 15 million years or so. Prior to this, the trough that holds the Snake River Plain was not there – the Rocky Mountains formed a continuous chain running from northwest to southeast. That trough has been excavated; the mountains literally blown into dust by massive supervolcano eruptions gradually eating eastward into the Rockies, with the debris spread far and wide across the continental US. This makes the Yellowstone hotspot the evil twin of the one beneath the Hawaiian Islands: above Hawaii, basaltic volcanism builds up mountains from the sea floor; above Yellowstone, explosive rhyolitic eruptions through continental crust destroys them.

Hawaiian and Yellowstone Hotspots

Hawaii and Yellowstone: the Yin and Yang of hotspot volcanism

Fifty years ago, people considered using nuclear bombs to blast through mountain ranges: little did they know that the planet had thought of it first, and on a scale orders of magnitude greater.

Categories: outcrops, photos, volcanoes
Tags: , , ,

Comments (15)

  1. Chris says:

    Excellent post, Chris.

    I understand that the Continental USA is largely decoupled from the Pacific plate motions, but can the Yellowstone hotspot be traced further back to any kind of ‘dog leg’ kink as seen in the Hawaiian hotspot volcanic chain?

  2. Jenny says:

    I like that volcanoes can have evil twins, I wonder what Yogi’s twin brother in Hawaii is called? Great photos too!!!

  3. Lockwood says:

    The initiation of the Yellowstone Hotspot was the probable source of the Columbia River flood basalts. There was an idea ~25 years ago that it might also be associated with the OR-WA ocean plateau basalts, which have been accreted as the basement of the Coast Range, but my impression is that the latter conjecture hasn’t panned out.

  4. Chris Rowan says:

    Either way, the kink in the Hawaiian hotspot track is about 50 million years old – the Yellowstone hotspot does not appear to have been active for more than the final third of that period.

    There is also still an ongoing debate over whether the Hawaiian kink is the result of a change in plate motion, or drift of the plume that is thought to create the hotspot. Paleomagnetic data seems to suggest at least a bit of the latter. Something to blog another day, perhaps?

  5. Bodach says:

    Wow, those topos really show the power of that caldera. Great piece; thanks.

  6. Stu Tanquist says:

    In his excellent book, A Short History of Nearly Everything, Bill Bryson notes that Yellowstone about due for its next big eruption, based on the frequency of past eruptions. Of course it could still be a long time by human standards—they don’t happen with the reliability of Old Faithful. Bryson noted that the upward movement of the Yellowstone caldera floor accelerated in recent years to several inches per year. Apparently that pace has slowed.

    Bryson also shares some fascinating anecdotes about geological activity in the park and related human tragedies.

  7. Burt says:

    Very nice. Saw something on Discovery(?) talking about the same info. Your write-up is far less sensationalist… (which is good, IMO).

    The location and age of the first in the line of hot spots on your topo would seem to correspond to my recollected location/time of the source for the Columbia River Basalt eruptions. Is it established that the two correspond or are related? I can’t recall from by tectonics course (some 20 years ago), if the two were linked.

    • Burt says:

      I just noticed Lockwood’s comment above which suggests my thought isn’t crazy… I guess it pays to read before commenting…

      Well, Chris, how about it? Wanna give us a write up of the CRB’s too?

  8. Brian Romans says:

    I still have never been to Yellowstone … I’m such a loser.

    Don’t forget to blog about this cool-sounding paper:

  9. Diane says:

    Chris, really good article. I do have a question about the Snake River plain. I can see from the map the line of the calderas and the resulting eastern part of the plain. The plain seems to curve up NW from the earlier calderas and I am wondering if you have any information on the cause of that part of the plain? Could it be from unrelated volcanic activity or a glacial feature?

  10. CherryBomb says:

    I never saw a map of the track before. Thanks. It seems to mark the northern edge of the Basin and Range suspiciously precisley, and 16.5 million years seems to be about right for extension starting at the earliest spot located. Is there any correlation of the start of spreading to time as you move west to east? I know one can date these valleys fairly well with fossils, but I have been out of touch.

  11. Chris Rowan says:

    With respect to the relationship between the Yellowstone hotspot and the Columbia River basalts: it seems to be something that is still being argued about. I suspect that this might be another front in the mantle plume wars – those who think the Yellowstone hotspot is due to a mantle plume are probably more in favour of a connection. What actual evidence there is either way other than philosophical inclination is going to require a bit more reading on my part – and the paper Brian lists looks like an interesting contribution to the debate.

    Diane – I’ve also been wondering about the western end of the Snake River Plain. This page suggests that it is a NW-trending graben (scroll down to ‘Geology of the Snake River Plain’ – that is, part of the Basin and Range.

    Cherrybomb – that’s an interesting question. I know that the lower crustal structure of the Basin and Range (the Moho is flat despite the localised surface extension) indicates that it might have been subjected to higher-than-usual temperatures. I also think that extension does indeed get younger to the East. But again, I’ll need to do more reading…

  12. Kerstin says:

    Hi Chris,
    this is a great post!
    I have been to Yellowstone earlier this year and have been wondering, too, if there would be a way to actually see the caldera. Like you, I couldn’t find a spot and was – well not disappointed (you simply cannot be disappointed by Yellowstone!), but a bit confused and somehow this whole volcano-thing never felt right. Now, with your explanations and the chain of “migrating calderas” I can imagine the process much better and it surely will stick in my mind now. Thanks.

  13. Brian R Catt says:

    I am not a geologist but have followed this and do read what I find. A few points here. The pictures were visible from the first satellite photos, or even from geological surveys. It was obvious the mountains were flattened by something as the ridge and basin structure just stopped one side and carried on the other. I heard about the Snake RIver Hot Spot years ago (60s?) as part of the “thinnest point on the earth’s crust” statistic. I suspect this is in part because the hotter rock cannot support the weight as well as the Vulcanism, although its not mentioned often by geologists (not physicists perhaps?). It is the case the height of mountains on Earth are limited by the compression stength of rocks and gravity, which is why Mountains are higher on Mars which is smaller but has less gravity, say. If you just look at the relief of the Rockies the very wide flat line at right angles to the N/S Ridge and Basin structure is a bit of a give away this is not any simple River Valley, but a continent dragging itself over a hot spot. Ouch! ouch!

    BTW although the Caldrera rim is hard to see the magma chamber isn’t, if you look in the right place………

    When they started looking they overflew the Lake with a thermal imaging camera trying to find a hot spot to account for its tipping. Didn’t find one, nice and uniform. Hmmm.

    Eventually someone decided to fligh higher and pan out to see if it was further away or there were more than one. That’s when they got a thermal image.It was there, but the size of the whole park. There are others nearby.

    Future generations a milion years or so ahead after the next one or two eruptions will find it easier to travel through the Rockies by road, and the Pacific weather will reach the mid West, as it currently gets to Yellowstone and delivers that nice powder to Jackson Hole’s micro climate. But then in another 1B or so Years America will hit Japan and started another Himalya perhaps so the game will change, as both plates ride over the Pacific plate I think? Hawaii will have disppeared under NYC as was.

    I love that the oil fields off the East Coast of South America (Venezuela and Brazil for example) and those off the West Coast of Africa (Nigeria and Angola) were laid down at the same time, just drifted apart while they developed and the Atlantic ridge pushed the Americas West on their 2B year voyage to Asia….. times are a changing, slowly.

    The opinion I have seen says that the far Western NW extension of the Snake River Valley is caused by other geological forces. Indeed you will find people claiming much of the Snake (should be Fish, a white man mis understood the Shoshone symbol for the Fish they lived on there for 11.000 years) is caused by the massive flash floods when ice age dams of ice and basalt entered the Snake RIver from Lake Bonneville, bursting the dam that existed at American Falls and reducing them to their current 50m or so..

    PS Unlikely to be humans left by the timne the next big one happens as we will have eradicated ourselves through selfishness, short termism and over population/pestilence/famine – or the Sun will change its output a tad and we’ll get frozen or cooked back to the Stone Age – if anyone can survive at all. The Dinosoars will wonder what happened to us when we had flying machines yet could not use our technology to manage our planet sustainably or protect civilisation against major disasters. Maybe an asteroid got them? Nah mate, selfish inflicted.

  14. Simon says:

    What is it that i can see 300 miles northeast of Montreal in Qubec on Google earth?
    It looks like a meteor crater to me.

    Links (3)
  1. Pingback: Geology Links for August 6th, 2010 | The Geology News Blog

  2. Pingback: Yellowstone: where did all the ash go? | Highly Allochthonous

  3. Pingback: Yellowstone: what lies beneath | Highly Allochthonous